1. Field of the Invention
The present invention relates generally to an apparatus for restraining cargo carriers such as pallets and containers within aircraft cargo bays. More particularly, the invention concerns a foot-operated restraint device comprising spring-loaded, fully retractable, interlocking pallet restraining pawls that are operable by the foot of the user, but are uniquely constructed so as to positively prevent accidental retraction.
2. Discussion of the Prior Art
Transport of cargo by large commercial aircraft is performed by placing the cargo into containers or onto pallets and then loading the containers or pallets into the cargo bay of the aircraft. For commercial cargo operations, the pallets weigh between about 2,000 lbs. to 13,000 lbs. Provided within the cargo bay are various mechanisms that are used to move pallets into and out of the aircraft and to restrain the pallets for ground and flight operation of the aircraft. Restraint of the pallets in flight is always a key safety requirement. Should any of the pallets shift in flight, a serious and unsafe out of balance condition could occur and serious damage to the cargo bay could result.
A key aspect of the cargo loading system is the pallet lock or end restraint. The purpose of the end restraint is to provide forward, aft and upward restraint of the pallets during flight and to fold down and out of the way during loading and unloading of the pallets. The typical prior art end restraint consists of a base, two transverse shafts connected to the base, an inner and outer pawl rotatably connected to the shafts, torsion springs to urge the pawls into an upward position, and either pins or plungers to connect the assembly to the aircraft floor. The typical end restraint operates by lifting the outer pawl to a vertical position. One of the torsion springs will then lift the inner pawl and snap both pawls into an upright position. The conventional prior art end restraint is collapsed by applying a downward force to the inner pawl. During normal cargo loading and unloading operations, the pawls are collapsed by the ground crew with foot pressure.
The end restraint design as described in the preceding paragraphs and specifically the pawl design dates back to the middle 1960""s and a number of different manufacturers currently manufacture and sell these types of devices. As a general rule the pawls of the various manufacturers are interchangeable and it is very common to find in operation an end restraint with an inner pawl manufactured by one company and an outer pawl manufactured by a different company.
It has recently been discovered through testing that under certain conditions, the end restraints can accidentally collapse during flight as a result of a pallet striking the backside of the inner pawl when there is no adjacent forward pallet within the cargo bay. It is the solution of this very serious problem that is at the heart of the present invention.
As will be better understood from the discussion that follows the end restrained apparatus of the present invention comprises a pair of interlocking pawls that are of a unique design so that they cannot be moved into a collapsed position by any initial pressure being exerted on the inner pawl from any direction. The pawls are released by the predetermined, considered sequential action of pushing the outer pawl down to an intermediate position, and then pushing down on the inner pawl. Unless this precise sequence is followed the pawls will remain securely locked in an upright position.
Another approach to solving the problem of accidental collapse of the end restraints is disclosed in U.S. Pat. No. 4,121,789 issued to Lent et al. This patent discloses a cargo latch, particularly for securing pallets or containers within aircraft compartment of the kind comprising two pivotal latch arms movable between an operative position in which one arm engages an item of cargo to be secured and the collapsed position in which the item of cargo is freed. In the Lent et al. construction, a catch element is provided in the base of the device for preventing the inadvertent movement of the latch arms from the operative to the collapsed position
U.S. Pat. No. 4,234,278 issued to Harshman et al. also discloses a locking device for securing air cargo units within aircraft cargo bay. The Harshman locking device comprises two pivotal latch arms of a relatively complex configuration only one of which is biased by spring means. The first pawl is held down in the retracted position by the weight of the second pawl. The outer or locking pawl is generally xe2x80x9cUxe2x80x9d shaped having a pair of spaced apart legs and a foot shaped outer crossmember for engaging the cargo carrier. The legs are pivotally mounted at their innermost extremities by means of pivot pins connected to the side members of the device base. The inner locking pawl has an inner base portion terminating in end portions, which are also pivotally mounted on the base by means of a transversely extending shaft. As the first and second pawls move into their upright position angularly extending surfaces provided on the two legs move into close proximity and function to lock the pawls in the upright position.
As will be understood from the discussion which follows, the apparatus of the present invention comprises a substantial improvement over the prior art and overcomes the various drawbacks of the prior art devices by providing an apparatus that is of a simple construction which is easy and inexpensive to manufacture. The apparatus is highly reliable in operation and includes novel locking means, which positively and effectively prevent accidental collapse of the cargo engaging pawls during flight. The locking means can be released only by the operator following a prescribed sequence of steps, which involves an initial downward movement of the outer pawl to an intermediate position. In this intermediate position, a locking protuberance of one of the pawls has been moved out of engagement with a locking notch on the other pawl so as to permit the sequential downward movement of the inner pawl into the lower position against the urging of a biasing means. When the pawls are in their upstanding position, a second biasing means continuously urges the locking notch into secure engagement with the locking protuberance.
It is an object of the present invention to provide an aircraft cargo carrier restraint device that is uniquely constructed so that it cannot be accidentally moved from extended, pallet locking position to a retracted position.
Another object of the invention is to provide a restraint device of the aforementioned character which embodies locking pawls of unique design that positively preclude movement of the pawls into a retracted position unless a specific sequence of operation is followed.
Another object of the invention is to provide a restraint device of the character described in the preceding paragraphs in which one of the locking pawls includes a locking notch and the other of the locking pawls includes a locking protuberance which is closely received within the locking notch so as to positively prevent accidental downward movement of the pawls into their lowered position.
Another object of the invention is to provide a restraint device of the aforementioned character in which the inner locking pawl includes a cam surface and in which the outer locking pawl includes a cam surface engaging shoulder which engages the cam surface of the inner pawl in a manner two urge the inner pawl into the lowered position as the outer pawl is moved toward the lowered position.
Another object of the invention is to provide a restraint device of the class described which is lightweight, compact, reliable in use and relatively simple and inexpensive to manufacture.